Utility service providers employ utility meters to meter or measure the usage of a utility commodity, such as water, gas, or electricity, by customers. Some utility meters furthermore meter energy that is delivered from one service provider to another. Recently, utility meters, including electricity meters, have employed microcontroller, microprocessor and/or digital signal processor technology to perform metering calculations. The use of such processing devices has facilitated more sophisticated data gathering techniques and has allowed for better analysis of commodity usage patterns and needs.
One particular architecture that enjoys significant use in electricity meters is based on a two processor core. Exemplary meters having such an architecture are described in U.S. Pat. Nos. 6,043,642 and 6,020,734, which are assigned to the assignee hereof and incorporated herein by reference. In this architecture, one processor is primarily used to perform raw energy, power, or rms calculations on instantaneous samples and the other processor is primarily used to control the meter components and to convert the raw calculations into final metering information that may be displayed or communicated externally. Variations on this core architecture include those that employ additional processors for other operations. It is also possible that a single processor may be used to accomplish the aforementioned tasks.
The two processor core architecture typically requires a variety of memory devices which are selected to address the varying memory needs of the processor based electricity meter. Random access memory (“RAM”) is typically used for interim calculations performed by the processors as well as for local storage of program code. RAM is often internal to one or more of the processor chips. Read only memory, also often internal to the processor chips, provides non-volatile, non-rewriteable storage for the main program code.
There are also several uses for a writeable non-volatile memory in an electricity meter. Such uses include the maintenance of metering data in the event of a power outage, the storage of calibration parameters, and potentially the storage of actual processor code that is field-replaceable. In addition, writeable non-volatile memory has been used for the storage of load profiling information, which comprises energy usage statistics for consecutive time slots over a month's duration or longer. Non-volatile memory is required to preserve the information in the event that power to the meter is interrupted.
Historically, writeable, non-volatile memory requirements have been filled, at least in part, by electronically erasable programmable read only memory (“EEPROM”) devices. However, such devices are limited in access speed, the number of usable write cycles, and power consumption. As a result, the use of EEPROM devices is preferably limited to only those applications in which rewriteable non-volatile memory is absolutely necessary. Thus, for example, the storage of metering data in non-volatile EEPROM is often limited in order to avoid unduly shortening the useful life of the EEPROM.
Moreover, for load profiling information in a meter, which may be written in excess of one hundred times per day, EEPROM technology is not typically used. Instead, battery-backed RAM arrangements have been employed to store load profiling information. The battery-backed RAM has the advantage of allowing substantially more write-cycles than EEPROM, and further has other advantages typically associated with random access memory. However, ordinary RAM loses its information in the absence of electrical bias power. Accordingly, to maintain load-profiling information in the event of a power interruption, batteries are employed as back-up bias power for the RAM.
FIG. 1 shows a prior art utility meter circuit 10. The utility meter circuit 10 may suitably be an electricity meter that includes a load profiling functionality. The meter 10 includes a processor 12, a measurement signal source 14, a primary power source 16, a volatile RAM 18, an EEPROM 20, a battery-backed RAM 22, a display 24, and a battery circuit 26.
The primary power source 16 is operably connected to provide bias power to the components of the utility meter circuit 10, including the processor 12, the measurement signal source 14, the volatile RAM 18, the EEPROM 20, the battery-backed RAM 22 and the display 24. The primary power source 16 may suitably be a power supply that is coupled to utility electrical power.
The measurement signal source 14 includes a circuit that is operable to generate commodity consumption signals that are representative of the use of a particular commodity to be metered. For example, the measurement signal source 14 may suitably be a source of electrical energy consumption signals. The processor 12 is coupled to receive the commodity consumption signals form the measurement signal source 14 and generate useful metering information therefrom. The processor 12 stores such information in the RAM 18 and periodically provides the information to the display 24.
The EEPROM 20 is coupled to periodically receive metering information from the processor 12. The EEPROM 20 stores such metering information in order to preserve the information in the event of a power interruption to the meter circuit 10. The EEPROM 20 may also store calibration parameters of the meter circuit 10. The battery-backed RAM 22 is employed to store commodity consumption statistical data, for example, load profiling information. Such information is typically too voluminous, and/or requires too many read-write cycles to conveniently be stored in the EEPROM 20. The battery circuit 26 is operably coupled to the battery-backed RAM 22 to provide bias power to the RAM 22 in the event of a power interruption.
The requirement of batteries to provide back-up power in the event of a power outage undesirably increases the size and component cost of the meter. Because of the increased inconvenience associated with the use of batteries, many meters include battery-backed RAM circuitry only when the meter application is specified for load profiling capabilities.
It is also noted that the requirement of multiple types of memories, such as RAM, ROM, EEPROM, and battery-backed RAM in meters has drawbacks related to software implementation, wiring and control. There is a need therefore, for more efficient memory configurations in electricity meters, as well as possibly other types of meters.